When I first start my car is sounds like it's revving up. It's really loud. Rpm gauge doesn't move. It only makes the noise when it is first started, like after it's been sitting all night, for about 20-30 seconds. After I turn it off for a few hours & restart it, the noise doesn't reoccur until next day. It's been happening for the about a month.
My car has 67000 miles.
My car has an automatic transmission.
I would inspect the area around the air filter for loose connections on the clamps or hoses. It is common for a lube center to leave something loose or not connected all the way.
If the RPMs are not raising then it sounds like some type of leak in the air intake system before the engine or an exhaust leak. If the RPMs were raising I would suspect a throttle body issue.
I’d suggest having the car inspected by a certified mechanic, such as one from YourMechanic, to diagnose the source of the noise you’re hearing and fix it accordingly. Good luck.